On Sept. 9, a mysterious explosion rocked a gathering of leaders of Ahrar al Sham, perhaps the largest Islamist rebel group in Syria. More than two dozen of its leaders were killed, including the group’s founder, Hassan Abboud. In the days after, many people bemoaned the loss of what the U.S.-backed Syrian Opposition Coalition called “moderates.” But history must still judge whether that is Abboud’s legacy.

I first met Hassan Abboud in the autumn of 2011, before he became Ahrar al Sham’s high emir. He had just been released from prison by the government of Bashar Assad in response to demands for political reform. As an organizer of some of those demonstrations, I thought it appropriate for me to meet some of the prisoners I’d helped free.

I found him to be polite, disciplined, very educated, with a degree in English literature. He spoke with a very low voice, and he struck me as shy.

The next time I met Abboud was at the beginning of 2012 in the mountains of my home region in the north of Hama province. By that time, the uprising against Assad was becoming bloodier, the demands for reform were being replaced by calls for regime change and officers who’d defected from the army were working to organize the rebel Free Syrian Army.

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By then, Abboud and his close friend Abdulnaser Alyassin, who would become Ahrar al Sham’s military leader, had established their organization and had set up a small base in the mountains. In those early days of the armed conflict, secular rebels outnumbered those such as Abboud who had religious agendas, and the two groups mixed easily in their mountain camps. I frequently ran into Abboud there and he came to know me too. From those early days, it was clear that Abboud saw no future for a secular Syria.

Once he told me, “I know, Mousab, you have leftist ideas about religion, but once we topple the Assad government, we will have channels to converse with you and people like you to invite them to the right path of religion.” He meant he would persuade me to leave my erroneous secular ways.

What I remember about that period is that the newly born Islamist group started to become rich very quickly. The Free Syrian Army was struggling to keep going by capturing small arms from Assad’s army, but that wasn’t the case with Abboud’s group, which seemed to receive huge amounts of support, whether money or weapons. One of my friends who is now a rebel leader told me that the moment the group announced itself in 2011 it got a big bag of money sent directly from Ayman al Zawahiri, the leader of al Qaida.

By late 2012, it had become clear to many of us in the secular opposition that Ahrar al Sham was stabbing us in the back. Foreigners began showing up in its ranks. Running into Saudis, Egyptians and Kuwaitis fighting with Ahrar al Sham became the norm. Ahrar al Sham also showed no interest in the local councils that had been established to promote democracy. It set up its own aid organizations and started to use mosques as schools. It distributed books and brochures that preached the conservative Salafi strain of Islam and held special classes in homes for women and children to learn Salafi teachings.

It was promoting international jihad, an approach that would end in making Syria a haven for all kinds of extremists.

Those of us who consider ourselves moderates and democratic did our best to stop their movement. Once I wrote a piece in a revolutionary paper that talked about how the austere Salafi version of Islam promoted by Abboud and his group was endangering the more tolerant Syrian version. Abboud didn’t like it. He wrote me on Skype saying, “Your piece is full of contradictions.” But he was also keen to show tolerance and was quick to add: “But this is your opinion and I do respect it.”

At some point, I think Abboud came to regret the moment he brought the first jihadi fighter to Syria. He was a Salafi dreaming of an Islamic state, but a Syrian one, not one imposed from the outside. He realized too late that his movement had become a Trojan horse that opened Syria to terrorists from all over the world.

Two weeks before he was killed along with most of the rest of the leadership of Ahrar al Sham, Abboud offered a series of tweets that criticized Dr. Eyad Qunaibi, a well-known Jordanian Salafi who supported the Nusra Front, al Qaida’s affiliate in Syria. That he offered direct criticism of Qunaibi’s support for Nusra – which Abboud referred to as the “bearded enemies” of the Free Syrian Army – was seen by many as a sign that Ahrar al Sham, always close to Nusra, was trying to distance itself from al Qaida.

On the day Abboud was killed, a new coalition of rebel groups was announced that implicitly recognized democratic values and rejected the Salafi extremist approach that Ahrar al Sham had so promoted. Rumor has it that so many Ahrar al Sham leaders may have gathered – 28 in all were killed – to consider whether to join the new coalition.

It’s still unclear whether Abboud, Alyassin and the others were assassinated or died in a freak accident. The lone survivor of the blast, Abboud’s brother Allam, died this Sunday, taking the secret of the explosion with him. But Hassan Abboud’s legacy of helping to introduce jihadi thought into the Syrian revolution is a real one. I can forgive him because I remember the beautiful days of the beginning of the revolution, when religion was not such a dominant feature. But I can’t guarantee that history will be so forgiving.